Skyrail bridges and precast concrete

With the Level Crossing Removal Project in full swing, new road and road bridges are taking shape all across Melbourne. But where does all of the precast concrete come from?

Siemens 779M on the up at Clayton

In the beginning

For many decades, precast concrete ‘Super T’ girders have been the goto design for new road and rail bridges.

Three of three straight approach spans in place, two lanes wide

With concrete poured into a steel mould, and steel reinforcing bar inserted, each beam is made offsite.

Field of precast concrete components at Westkon casting yard

Trucked to the bridge site.

Semi-trailer transporting oversize precast concrete super T-girders around the corner of Francis Street and Hyde Street, Yarraville

And lifted into place by crane.

Packing up the cranes used to install the eastbound carriageway of the Melton Highway bridge at Sydenham

Enter ‘Skyrail’

In 2016 it was announced that all nine level crossings between Caulfield and Dandenong would be eliminated by the construction of an elevated railway line. However there was one problem – the rail corridor between Caulfield and Oakleigh was too narrow for conventional bridge building techniques.

VLocity VL44 on a down Gippsland service at Carnegie

The solution – a dedicated casting plant was established at Pakenham.

Casting plant for concrete viaduct segments at Pakenham

It all starts with a cage of steel reinforcing mesh.

Steel reinforcing cages for precast concrete viaduct segments

Concrete is then poured, giving a short segment of bridge.

Concrete viaduct segments for the Carnegie-Hughesdale section at the casting plant in Pakenham

They are then trucked one by one to the assembly site at Murrumbeena station.

Concrete bridge segment waiting on Warrigal Road before delivery to the assembly site at Murrumbeena station

Where they are assembled into completed beams.

Pair of portal cranes at the Murrumbeena station assembly site

And lifted the top of the completed bridge.

Pair of portal cranes at work moving a completed bridge span at Murrumbeena station

Where they are collected by a straddle carrier.

Two gantry cranes and the straddle carrier ready to go at Murrumbeena station

To deliver them to their final home at the end of the bridge.

Straddle carriers at work placing viaduct spans between Murrumbeena and Carnegie stations

Between May 2017 and April 2018 a total of 174 bridge spans were delivered – each ranging from 280 to 420 tonnes, with the straddle carrier travelling more than 260km back and forth along the rail line.

Some breathless boasting

The use of the straddle carrier and gantry crane solution was seen as innovative.

The new skills, processes and protocols associated with this national first have entailed an extensive amount of behind the scenes activity, including a comprehensive training programme.

Simon explains: “We’ve trained approximately 300 workers to operate the carrier, gantry cranes and support beams, as well as cast and tension the spans that make up the rail deck. It’s not insignificant from an industry perspective as we will retain this knowledge in Australia along with a whole range of highly transferrable skills.”

But the rail viaducts at the Noble Park end of the project used conventional super T beams.

Twin single track viaducts in place at Corrigan Road, Noble Park

As did the viaduct at Clayton.

Concrete slab track at the new elevated station at Clayton

With the straddle carrier and gantry crane meeting an inglorious end dumped in a yard at Sandown Park racecourse.

Components of the 'Skyrail' straddle carrier and gantry crane stored at Sandown Park racecourse

The reason?

And the new hotness – U-Trough beams

By 2019 a new, much simpler design of rail viaduct had taken over – the U-Trough.

Down end of Hawkstowe station, viaducts pass over public space

With cleaner lines, the design also reduced the total height of the final viaduct, by containing the rail track inside the bridge structure itself.

Signals COB505 and COB515 at the down end of Coburg station

The first example was the Mernda line extension, and quickly followed by the level crossing removal at Skye Road on the Frankston line.

With the beams manufactured at the NVC Precast yard in Kilmore.

Google Maps

The plant having a 115 lineal metre radiant heat cured bed fitted with external vibrators, two 1800 tonne slow release stressing jacks, and two 80 tonne x 40 metre span portal gantry cranes covering a working area of 8000m2.

NVC Precast photo

As with all precast concrete, the rebar is the first step.

NVC Precast photo

With the resulting beams being stacked in the yard.

NVC Precast photo

Until they leave the site by road.

NVC Precast photo

Cranes are used to lift the beams from the truck, and into place to make a bridge.

Crane erecting 'U' trough sections at the down end

Work able to be completed with minimal disruption to rail services.

X'Trapolis 9M trails an up service out of Lilydale

Even on narrow sections of rail corridor, like that between Bell and Preston stations.

Only the up track viaduct in place at between Bell and Preston stations

Some early projects used preassembled U-trough beams.

NVC Precast photo

Delivered via convoluted routes.

But other projects have seen them delivered in two halves, to reduce the total weight of the load.

Section of 'U' trough delivered by road and waiting to be lifted into place

The beams then tied together on site.

Rebar in place between the two halves of the U-trough viaduct, waiting a concrete pour

With concrete poured in place.

Concrete pour completed between the two halves of the U-trough viaduct, section of formwork awaiting removal

The list of LXRA projects that have used U-trough bridges is long and growing, including:

  • Mernda Rail Extension
  • Skye Road, Frankston
  • Seaford Road and Carrum
  • Abbots Road and Greens Road, Dandenong South
  • Werribee Street, Werribee
  • Toorak Road
  • Reservoir
  • Hallam
  • Lilydale and Mooroolbark
  • Coburg and Moreland
  • Preston and Bell
  • Deer Park

(And probably a few more that I’ve missed!)

Footnote: more on U-troughs

In September 2019 Roads & Infrastructure published a piece on U-troughs.

The Level Crossing Removal Project will see 75 level crossings throughout Melbourne removed by 2025 in order to increase safety, reduce travel times and better connect communities across the city.

So far 29 level crossings have been removed and completed across Melbourne, including one at Skye Road in Frankston.

For the first time in Australia, the Level Crossing Removal Authority, principle contractor, designers, engineers and NVC Precast worked together to deliver the elevated rail using prefabricated concrete U-Trough beams.

The design of the Skye Level Crossing Removal used 24 prefabricated concrete U-Trough beams, that were over 6 metre wide, 30 metres in length and weighing an impressive 280 tonnes to construct the rail bridge using Rapid On-Line Construction techniques. This reduced the rail occupation period and sped up the overall construction of the project for the benefit of the community.

NVC Precast were chosen to manufacture the U-Trough beams based on their experience in precast and the L-Beams used for elevated rail for level crossing removal.

NVC Precast were able to manufacture and store the beams at their precasting facility in Kilmore Victoria, coordinating delivery to arrive just in time to be erected on site.

The U-Trough beams were produced by stitching two precast concrete L-beams together which were between 25 and 31 metres long with masses up to 120 tonnes each, creating a single unit that weighted up to 280 tonnes.
The L-Beams were positioned to be stitched out in the yard.

The project involved extensive planning to create the forms and casting beds for the manufacture of the beams, the plant to transport them to site, and to create the infrastructure for the stitching and loading at the precast yard.

NVC Precast Construction Manager oversaw the casting of the L-Beams and the process for the stitching of the U Troughs which took four weeks to complete in April 2018.

NVC Precast manufacture up to four L-beams at a time casting 140 to 160 m3 to produce 12 L-Beams per week. To create a single segment U-Trough Beam, 50% of the L-Beams were rotated 180˚, matched positioned on pedestals for the joining stitch to be cast. The rotation and match positioning was achieved using GPS guided SPMT and 80 tonnes Portal Gantry Cranes for the final touches.

The U-Trough beams were stored at NVC Precast’s Kilmore site before transporting to site and final installation into the elevated rail viaduct.

NVC Precast had to ensure that the load out facility it constructed allowed for 2 No. 12 axle Platform trailers to be accurately positioned under the 280-tonne segments for loading and chaining down.

Mr. Bell says the recent redevelopment of the NVC Precast site has created plenty of storage area for both storage and ancillary works such as painting, attaching handrails, barrier rails and temporary walkways.
The U-Trough beams were positioned by stitching two precast concrete L-beams together.

“This allows us to work closely with our clients to provide both precast concrete elements and solutions to some of the common construction problems, such as working at heights,” Mr. Bell says.

“As you are working beside a live rail line, rail upgrade requires closing the rail line every time you want to install the beams, which causes major disruption to rail traffic. With the L beams joined as U troughs off site, you take all the construction activity related to splicing off site and do it when the rail is still open. Then you can close the rail for significantly shorter periods just to install the complete U trough beams.”

Mr. Bell says the U-trough is a very efficient design as the trains operate within the walls of the beams which provides a much lower profile and is more aesthetically pleasing elevated structure.

“The offsite fabrication of the U Trough beams for the Skye project was a great initiative by the main contractor and provided many benefits to the overall onsite construction process, through the benefits of both off site precast techniques allowing rapid installation, great quality control, a reduction in the overall construction footprint, and eliminated a lot of safety issues.”

And structural engineer Daniel Pang published a paper in 2021 on the use of U-trough viaducts on the Toorak Road Level Crossing Removal Project, and how they differed from the standardized design developed by the LXRA’s U-Trough Joint Design Group.

The Toorak Road Level Crossing Removal Project (LXRP) removed and replaced the existing level crossing with two U-Trough elevated rail viaducts. The design drew on what had been developed for previous LXRP designs but introduced refinements and accommodated the project specific features.

The primary objective with the development of the standard U-Trough was to accommodate the online construction requirements of the overall LXRP program of works throughout metropolitan Melbourne for which speed of construction along existing rail corridors is critical.

The alliances teams participating in the LXRP works had decided to adopt a U-Trough solution as opposed to previously developed and tested local market solutions such as Super T beams and box section. This decision was been based upon the fact that the U-Trough solution had gained acceptance from stakeholders and was regarded as satisfying the design, construction, operational and maintenance objectives of rail infrastructure.

The U-Trough solution provides many advantages over other systems such as Super-T and concrete box girder sections. This solution enables minimisation of the height difference from the soffit level to the top of track and hence provides a lower vertical grade separation height and minimises the required earthworks. In the event of derailment, the train will be contained within the structure, which provides a significant safety benefit.

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8 Responses to “Skyrail bridges and precast concrete”

  1. Andrew says:

    Very interesting. I guess whichever structure has to be transported to sites, they are too large to be transported by train.

    Victoria must be somewhat expert at level crossing removals, that will vary from one site to another. It is a pity we can’t build trams and trains suitable for the rest of the Australia.

  2. H says:

    U-troughs were first designed (and constructed) at Mernda not Skye Road. Skye Road was the first place they were installed as a single U rather than two Ls though.

  3. Sergio says:

    T beams photos above are from Westkon precast , you can see the truck logo , Westkon is the biggest in precast , providing more than 200 jobs , safety is above anything, not like all does cutters , they yards are filthy and unsafe , and they explore all they workers as not paying the right wages to is workers. So if you guys want to do a story in precast get you fact right first , and post photos from the actual company ( I know y you didn’t they are to dirt for you to show ) . If anyone zoom in in the photos the one with T beams hanging you will see Westkon logo on it and the photo with the truck Westkon logo on it . Then stop talk . And if you gonna post something make sure your story will match with your photos . Our you to a chame to show the right company photos . If you want a good story to talk about , get a company pays is workers right , EBA rates and doesn’t take advantage of is workers using ABN holders , and not paying , what any workers will get across border in precast . That y you get government jobs because you take advantage of hard working Australians. Shame to you NVC and government.

    • Marcus Wong says:

      My photo of the Westkon truck is at their yard beside the Sunbury line in Albion, it seems they only cast smaller bits and pieces there, with the super-T beams coming from their larger yard beside the railway at Melton.

  4. […] the precast concrete for the ‘Skyrail’ bridges were initially cast 50 kilometres away at Pakenham, and are now cast 70 kilometres away at […]

  5. […] The approach at the city end is a now standard U-trough viaduct. […]

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